1.Surfactants for fracturing measures
Fracturing measures are often applied in low-permeability oilfields. They involve using pressure to fracture the formation, creating cracks, and then propping up these cracks with proppants to reduce fluid flow resistance, thereby achieving the goal of increasing production and injection. Some fracturing fluids are formulated using surfactants as one of their components.
Oil-in-water fracturing fluids are formulated from water, oil, and emulsifiers. The emulsifiers used include ionic, non-ionic, and amphoteric surfactants. If thickened water is used as the external phase and oil as the internal phase, a thickened oil-in-water fracturing fluid (polymer emulsion) can be prepared. This type of fracturing fluid can be used at temperatures below 160°C and can automatically demulsify and discharge fluids.
Foam fracturing fluids are those with water as the dispersion medium and gas as the dispersed phase. Their main components are water, gas, and foaming agents. Alkyl sulfonates, alkyl benzene sulfonates, alkyl sulfate esters, quaternary ammonium salts, and OP-type surfactants can all be used as foaming agents. The concentration of foaming agents in water is generally 0.5–2%, and the ratio of gas phase volume to foam volume ranges from 0.5 to 0.9.
Oil-based fracturing fluids are formulated using oil as the solvent or dispersion medium. The most commonly used oils in the field are crude oil or its heavy fractions. To improve their viscosity-temperature performance, oil-soluble petroleum sulfonates (with a molecular weight of 300–750) need to be added. Oil-based fracturing fluids also include water-in-oil fracturing fluids and oil foam fracturing fluids. The former uses oil-soluble anionic surfactants, cationic surfactants, and non-ionic surfactants as emulsifiers, while the latter uses fluorine-containing polymeric surfactants as foam stabilizers.
Fracturing fluids for water-sensitive formations are emulsions or foams formulated using a mixture of alcohols (such as ethylene glycol) and oils (such as kerosene) as the dispersion medium, liquid carbon dioxide as the dispersed phase, and sulfate-esterified polyoxyethylene alkyl alcohol ethers as emulsifiers or foaming agents, used for fracturing water-sensitive formations.
Fracturing fluids for fracture acidizing serve as both fracturing fluids and acidizing fluids, used in carbonate formations where both measures are carried out simultaneously. Those related to surfactants include acid foams and acid emulsions; the former uses alkyl sulfonates or alkyl benzene sulfonates as foaming agents, while the latter uses sulfonate-type surfactants as emulsifiers.
Like acidizing fluids, fracturing fluids also use surfactants as demulsifiers, cleanup additives, and wettability modifiers, which will not be elaborated on here.
2.Surfactants for profile control and water plugging measures
To improve the effectiveness of water flooding development and inhibit the rate of increase in crude oil water cut, it is necessary to adjust the water absorption profile in injection wells and take water plugging measures in production wells to increase production. Some of these profile control and water plugging methods often use certain surfactants. The HPC/SDS gel profile control agent is prepared by mixing hydroxypropyl cellulose (HPC) and sodium dodecyl sulfate (SDS) in fresh water. Sodium alkyl sulfonate and alkyl trimethyl ammonium chloride are respectively dissolved in water to prepare two working fluids, which are injected into the formation successively. The two working fluids meet in the formation, producing alkyl sulfite precipitates of alkyl trimethyl amine, which block the high-permeability layers. Polyoxyethylene alkyl phenol ether, alkyl aryl sulfonate, etc., can be used as foaming agents. They are dissolved in water to prepare a working fluid, which is then alternately injected into the formation with a liquid carbon dioxide working fluid. This forms foam in the formation (mainly in high-permeability layers), causing blockage and achieving the profile control effect. A quaternary ammonium salt-type surfactant as a foaming agent is dissolved in a silicic acid sol prepared from ammonium sulfate and water glass and injected into the formation, followed by the injection of non-condensable gas (natural gas or chlorine gas). This first generates foam with liquid as the dispersion medium in the formation, and then the silicic acid sol gels, resulting in foam with solid as the dispersion medium, which blocks high-permeability layers and achieves profile control. Using sulfonate-type surfactants as foaming agents and high molecular compounds as thickening and foam-stabilizing agents, and then injecting gas or gas-generating substances, water-based foam is generated on the surface or in the formation. In the oil layer, a large amount of surfactant moves to the oil-water interface, causing foam destruction, so it does not block the oil layer and is a selective oil well water plugging agent. Oil-based cement water plugging agent is a suspension of cement in oil. The surface of cement is hydrophilic. When it enters the water-producing layer, water displaces the oil on the cement surface and reacts with the cement, causing the cement to solidify and block the water-producing layer. To improve the fluidity of this plugging agent, carboxylate-type and sulfonate-type surfactants are usually added. Water-based micellar fluid plugging agent is a micellar solution mainly composed of ammonium petroleum sulfonate, hydrocarbons, alcohols, etc. When it encounters high-salinity water in the formation, it can become viscous to achieve the water plugging effect. Water-based or oil-based cationic surfactant solution plugging agents, which are mainly composed of alkyl carboxylate and alkyl ammonium chloride surfactants, are only suitable for sandstone formations. Active heavy oil water plugging agent is a heavy oil dissolved with water-in-oil emulsifiers. When it encounters water in the formation, it produces a high-viscosity water-in-oil emulsion to achieve the purpose of water plugging. Oil-in-water plugging agent is prepared by emulsifying heavy oil in water using cationic surfactants as oil-in-water emulsifiers.
Post time: Jan-08-2026